This function always returns 1, but gcc misses the optimization:
int foo(unsigned char x)
{
return (x+1) != 0;
}
fold-const.c converts the comparison to "x != -1", but that's it.
shorten_compare() in c-common.c would optimize it, but it doesn't get called.
fold-const.c has similar code on lines approx. 9307..9454 but is less general
(and uglier) than shorten_compare() and misses this case. tree-vrp.c says x is
varying and doesn't help out either.
An example of this construct is line 527 of libmudflap/mf-runtime.c
if (*optstr+1)
That looks like a buglet, by the way.
--
Summary: Missed optimization of comparison with 'limited range'
Product: gcc
Version: 4.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: trt at acm dot org
GCC host triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27007
